SAN FRANCISCO -- Biking or walking to work may boost fitness and reduce risk for obesity and cardiovascular disease, researchers affirmed.

Action Points

Explain to interested patients that getting sufficient physical activity -- whether recreationally or as part of a daily commute to work -- has health benefits.

Note that self-selection bias might have been a factor in the study findings and that the observational data could not determine causality.

SAN FRANCISCO, July 13 -- Biking or walking to work may boost fitness and reduce risk for obesity and cardiovascular disease, researchers affirmed.

Men who got to work by such 'active commuting' cut the risk of obesity in half and significantly reduced triglyceride levels, blood pressure, and insulin levels compared with riding to work, Penny Gordon-Larsen, PhD, of the University of North Carolina at Chapel Hill, and colleagues reported in the July 13 issue of the Archives of Internal Medicine.

These effects in a large cross-sectional study were accompanied by a significant increase in fitness among both men and women who walked or biked to work.

The gender difference was likely because men in the study got a higher "dose" by commuting farther than women, the researchers said.

While the results weren't surprising given the well-established link between leisure-time exercise and heart health, Dr. Gordon-Larsen's group noted that these results provide the evidence to support public policy changes.

Effective policies, such as those that make neighborhoods safer and easier for biking and walking, "will have the dual benefits of increasing population health and in reduction of greenhouse gas emissions," they suggested.

They cautioned, though, that the observational data could not imply a causal role for commuting in promoting cardiovascular health and fitness, particularly because there may be important differences between people who choose to actively commute to work and those who don't.

"Yet, our results suggest that any portion of the commute made by walking or biking is important for maintaining or improving health, regardless of the direction of causation," Dr. Gordon-Larsen's group wrote.

Because most prior research has been limited to Scandinavia or looked only at leisure-time activity, Dr. Gordon-Larsen's group analyzed population-based data from the Coronary Artery Risk Development in Young Adults (CARDIA) study.

Of the 2,364 adults in that study who worked outside the home during 2005-2006, 16.7% reported walking or biking as part of their commute.

The length of the commute appeared to play a role in the low rate of physically-active commuting: Active commuters averaged 5 miles and 20 to 17 minutes for men and women, respectively, to get to work compared with 10 to 14 miles and 20 minutes among other commuters.

After controlling for other differences between the two groups -- age, race, income, education, smoking, and level of physical activity excluding walking -- active commuters had significantly higher levels of fitness, measured in endurance on a treadmill test (50.0 extra seconds for men, P<0.001, and 28.77 for women, P=0.001).

Body mass index was significantly lower for men who walked or biked to work as well (BMI ratio 0.95, P<0.001), though not for women.

Obesity was 50% less likely among male active commuters than other men (P=0.001).

Although the point estimate for risk was in the same direction for female active commuters, the effect was not significant (odds ratio 0.91, P=0.59).

For the cardiovascular risk factors, results again favored walking or biking to work for men:

Mean triglyceride levels (ratio 0.88, P=0.02)

Mean fasting insulin (ratio 0.86, P<0.001)

Mean diastolic blood pressure (difference -1.67 mm Hg, P=0.03)

Higher HDL cholesterol, though in the partially adjusted analysis only (ratio 1.05, P=0.04)

For women, none of the lipid, blood pressure, or insulin measures were significantly different between groups.

Analyses of only those living very near their job -- within two miles -- yielded largely similar results.

But controlling for BMI eliminated significance of all relationships, suggesting this was a mediating factor, the researchers said.

They cautioned that reverse self-selection bias might have been a major limitation of the study, since being healthy and more inclined to be active may make a person more likely to walk or bike for transportation.

However, Dr. Gordon-Larsen's group noted that "many of the associations in this study remained after controlling for other forms of physical activity."

They called for further study to determine the "dose" of active commuting needed to produce the health benefits seen in their analysis.

The CARDIA study was supported by National Heart, Lung, and Blood Institute (NHLBI) grants. Analysis was supported by grants from the National Cancer Institute and National Institute of Child Health and Human Development. Additional funding was provided by the National Institutes of Health; the Carolina Population Center; and contracts with the University of Alabama at Birmingham, University of Minnesota, Northwestern University, and Kaiser Foundation Research Institute.

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